Line printer



Aug. 13, 1963 N. B. WALES, JR

LINE PRINTER 2 Sheets-Sheet 1 Filed April 7, 1961 INVENTOR.

Aug. 13, 1963 N. B. WALES, JR

LINE PRINTER 2 Sheets-Sheet 2 Filed April 7, 1961 IL-" L '2,

United States Patent 3,10%,440 LINE PRINTER Nathaniel E. Wales, J12,Sharon, COHIL, assignor to The Metrodynamics Corporation, a corporationof New Jersey Filed Apr. 7, 1961, Ser. No. 126,358

10 Claims. (Cl. lei-+93) This invention relates to an improved controlsystem for printing mechanisms having a buffer memory adapted to receivecoded information in series or parallel form, and to print it on a page,one line at a time. g It is well known in the printer art to use acoaxial row of printing wheels which are positioned and then impactedsimultaneously andselectively by a row of harm mers through the copypaper to print a line of numeric or alphanumeric characters at a time.

However, the amount and cost of equipment heretofore required to storethe coded information representing the line of print and then to decodeand distribute it so as rapidly to position such multiple adjacent printwheels has been so great as to preclude the economic use of such asystem in any medium size or medium speed computer or communicationsystem.

The present invention makes possible an inexpensive and. reliablecomputer output printer which will print on the order of 4 to 5 linesper second corresponding to. 4 to 608 characters per second depending onthe number of columns per line desired. H p

The means taught by my invention to accomplish this object includes thenovel combination of a gaseous discharge tube memory used in conjunctionwith a plurality of photoelectric comparators and optical decodingdisks.

The principle of my invention is to provide a separate code-memory, acomparator, and a stopping device for each print Wheel, so that as allof the print wheels in urison are permissively allowed to scan. throughall of the available characters, each print wheel will be indiv-idua-llystopped when its comparator senses agreement between the storedcharacter code and the code through which the permissive device ismomentarily scanning. When the scanning operation is completed, theselected hammers simultaneously print the line composed by the stoppedtype wheels. Subsequently, the paperQis adv-anced, and'the print wheels,hammers, and memory are restored to begin a new cycle :of line printing.

Using conventional flip-ilopor magnetic core memories, together withelectronic comparators, such a system would be prohibitively expensivefor a multiple column printer. My invention, however, is devised toallow low cost memory devices to be an integral part of the comparators.This is done by using for each memory device the well known memoryproperties of gaseous :dischar-ge diodes, and optically arranging thecoded pattern \oflight generated by these gas diodes to fall on a singlephotoelectric cell through a coding disk shutter synchronized with thescanning mechanism of the print Wheels. This combination of a codedgroup of electro-optic memory elements with a common photoelectricobserver thus constitutes an or gate which signals a successful comparison between memory and print wheel code disk by 3,100,440 PatentedAug. 13, 1963 the required equipment would be more than doubled so that,for instance, a six bit code would require twelve tubes behind twelvechannels of coded windows with 13.11 arrangement for each code bit tolight one tube for a 1 and another fora 0. t

t My invention, however, obviates this complication by selecting a codesequence on the print wheel decoding disks which in the normal directionof selective scanning presents no codes which are not initiallycorrectly compared by the foregoing darkness criteria, thus permittingthe use of the smaller number of channels (in the foregoing case, six).

In the preferred embodiment of my invention, the computer which is tocontrol the subject line printer is pro.- vided with a six binary bitfeed back signal on six wires which tells the computer continuously atwhich position a continuously running distributing commutator iscurrently located. This commutator sequentially enables groups of sixneon memory tubes to receive ignition from a six wire printer input busthrough which the computer can fill up the neon buffer memo y with theinformation representing a line of characters.

A logical or gate is provided to monitor the six wire writing bus. Also,a second distributing commutator synchronized with the foregoingenabling commutator is arranged to distribute the signals from theforegoing or gate to a hammer-enabling memory device for each column ofthe printer. In this way, when the time comes to impact the hammersagainst the print wheels in the printing cycle, only those hammers underwhich a coded character was selected will fire, thereby preventingsmudges at the columns requiring blank spaces.

Both the hammer enablying memory devices and the print wheel stoppingdevices may profitably employ the Magnetic Release S trncture disclosedin my co-pending application No.;66,462, filed November 1, 1960, and forthis reason the preferred embodiment here disclosed incorporates thishigh speed release system. i One object of my invention is to provide alow cost high reliability design for line printers suitable forcommunication channels and computer read-out.

A second object is to provide a combination bufior memory and comparatorfor the low cost distribution,

storage, aud read-out, of binary information.

i A third object is to provide a combination memorycomparison system inwhich the logic of writing 1s acthe photoelectric conditioncorresponding to the absence complished by electricalmeans and inWhichthe logic of reading and comparison is accomplished byphotoelectric means. p ,7 q

A fourth object is to provide a method of construction for analog todigital coding masks which achieves compactness .by permitting severalreading stations to share their lower order coding tracks.

Other objects are implicit in the accompanying specifications andclaims.

In the drawings: FIG. 1 is the schematic diagram of the preferredembodiment of my invention;

FIG. 2 is a section through 22 of FIGURE 3 normal to the axis of anoptical decoding-comparator disk of my invention showing thephotoelectric comparison reading heads for four printing columns sharingthe same decoding disk;

FIG. 3 is a section through 3-3 of FIG. 2;

FIG. 4 is a section through 4-4 of FIG. 3;

FIG. 5 is a view in elevation through 55 of FIGURE 6 showing thepreferred magnetic release structure used for control and memory in myinvention; and

FIG. 6 is an end view through 6-6 of FIG. 5.

The line printer depicted in FIG. 1 consists of a plurality of adjacentcoaxial pint wheels 1 each bearing a or starting, position.

a, mouse font of character type faces 2 which protrude from the I viec'tory which embraces pin 15, secured to'wheel 1, so I that when shaft3 is in the home position shown, pin 15 is entrapped-between this fingerand the fixed stop finger 16, thereby forcing print wheel 1 also to bein its home,

When shaft 3 is rotated counterclockwise away from its home position, itfrictionally, and without slippage carries with it all of the typewheels 1. Each type wheel 1 is provided with a stopping catch lever 4which is urged by its spring 6 to rotate about pivot 5 so as toengage-one'of the teeth formed by type faces 2.

However, each lever 4- is normally restrained against the force ofspring 6 to be out of engagement with the teeth of wheel 1 by thearmature secured to it by pivot pin 7, and composed of pole piece 9 andpole piece 10, which embracethe permanent ceramic magnet bar 8. Thepoles 9 and 10 of this permanently magnetized armature normally areattracted to the stationary soft iron iingegrs of corresponding washer14 to slip relative to wheel 1 until shaft 3 comes to the end of itsforward or setting rotation.

ll 5 V At this moment, the hammers 49 corresponding to each column to beprinted are actuated to rotate about their common spindle shaft 41 so asto impact the printing ribbon 39 against the'paper 1 8, andfag-ains tthe selected corresponding type faces 2, thereby printing the selectedline of characters on the paper 18.

After the line is printed, the shaft 3 reverses and 'ro tates clockwiseto return all of the print wheels 1 to'their original home positionsshown. f

The 'motivepower for the foregoing rotary reciproca- 1 tion of shaft'3jis supplied by the continuously running motor 68' which drives shaft 66through'reduction gear 67;

The continuous rotation of shaft 66-. may be'coupled by the onerevolution clutch 64- to the drive shaft 32 on receipt of a commandsignal by electromagnetic release coil 65 Shaft 32, in turn, is suitablyjournalled, and has SSClJIGdlO it thecam-cnank'disk 29, which is coupledby link 27 and pivot pins 28 and 26 to the sector gear 25,

which in turn is journalled on fixed pivot shaft 31. 'Consequently,during the first half of the revolution of disk-29, link'27 drivessegment gear into approximately QO" of clockwise rotation; while duringthe, sec- 0nd half of the revolution of disk 29', segment 25 executescounterclockwise rotation. r V This sinusoidal angular displacementof-gear sector 25 t r is multiplied by the ratio between pinion 33,secured to shaft 3, and the gearseotor 25 to which it is meshed. Thisratio is chosen to displace shaft 3 and its friction fingers 14 throughthe full arc occupied by the available type faces 2. I

At the end of the clockwise reciprocation of shaft 3, cam surface 30 ondisk 29 is designed to lift cam followeri on arm 36 so as to produce aclockwise displacement of shaft Si -against spring 33. The consequentmomentary angular reciprocation of cam follower shaft 37 is communicatedby the mechanical coupling produce two sequential operations, namely:actuation of.

means 33 to levers 58 and 38, and also to normally closed switch '79 toopen it momentarily.

Thelevers 58 use the foregoing reciprocation of shaft 37 to reset any ofstop-levers 4 which may have been released into magnetic engagementbetween 'armatures 9-1 and the stationary magnetic circuits -11.

The levers 57, which are also actuated by the mechanical connection 38,utilize this eammed reciprocation to the selected hammers 46 (first),and reset oflthe selecting armatures (second). 7 7 J lslechanicalconnection 33 is arranged to cause the first half of the reciprocationof shaftffi to produce a counterclockwise displacement of levers 57, andto cause the second half of reverse reciprocation to produce a clockwisereturn of levers57; I

During the first portion of the counterclockwise motion of levers 57,levers 43, which are pivotally secured to the hammer levers ltlby studs42, are urged to the left by links 44 which interconnect levers 43 and57.

If the bottom of a lever 43 is restrained from leftward motion (FIG. 1)by its engagement with the notch 47 of lever 45, then the foregoingleftward motion of link 44 will produce aclockwise moment on its hammerlever all. This will overcome spring 44, which normally holds hammer 40against stop bar 112, and impact the hammer face onthe printing ribbon39, paper 18, and character type face 2, to cause printing at thecorresponding columnar position. 7 i

Conversely, if the bottom of lever 43 is unrestrained by virtue of theabsence'of a release signal to coil 54 for lever 45 so that notch 47does not engage lever 43, then 57, they engage any of memory levers 45which had been released, and carry themagainst the action of springs 427 into the reset position in which theirarmatures 56 5 1 52 are inmagnetic engagement with their stationary magnetic circuits 53. I V I Itis evident that the magnetic release structure for lever 45 is identicalwith that of lever 4,"and so the'detailed views 'of FIGS. 5 and 6 applyto both. As expounded in thecopending application cited, this structure,in which i a source of high coercive, low-permeability magnetomef tiveforce islocated in the armature and supplied with a magnetic shunt byits distributed poles, providesa very 1 high rate of change of flux withincreasing gap separation. Consequently, a very short low energy pulsesignal will elfect release of such a device. I I v a The paper 18 onwhich the line printing is effected together with carbon copies ifdesired) is suitably guided, and is clamped for line advancement andformat control between the resilient rollers 19. A ratchet'250 securedto one roller 19 is provided, so that at the end of the recip rocativerotation of sector 25, the pawl 21 which is.pivotally secured to sector25 by stud 214, as guided by pin 22 and biassed by spring 23,may advanceratchet 2%) by one teeth, thus comprising an automatic line feed. Cam63, secured to shaft 32, is followed by lever 66, pivoted at stud 61 andbiassed by spring 62, so that switch 5%, actuated bylever 60, is closedduring the first half of the revolution of shaft 32,.and open during thesecond (plus a home position) is provided, which thus requires I a sixbit binary code to specify uniquely a selected character.

The buifer memory component taught by my invention for registering thesix bits representing the code for each columnar character is a gaseousdiode glow tube 83 characterized by having a substantially higherignition, or firing, potential than the glow, or running, potentialappearing across it after firing and during conduction.

The foregoing electrical properties permit groups of six of such glowtubes 83 to be connected to a common signal bus 82 in such a way thatparallel groups of six bit code signals emitted serially from a computer92 (or similar signal source) can be distributed one column at a time toignite only those glow tubes called for by the code groups, until a linefull of binary character information has been accumulated in this bufiermemory in the form of glow discharges. it

As described in subsequent detail, the light from these groups ofelectrical glow discharges is then used optically to repeatedlyinterrogate a decoding mask 86, which signals the code corresponding tothe typeface which is momentarily moving into registration with thehammer position during the scanning rotation of the type wheels 1 in theselection phase of the print cycle.

When the remembered buffier code, represented by the pattern of glowdischarge for a given column, compares correctly with the pattern of themoving decoding mask, a signal is generated by the transition of aphotoelectric cell 85 from illumination to darkness, since this cell hasbeen arranged through the use of a light pipe 84 to operate as an orgate, by simultaneously looking through the mask at all the glow tubesin its group of six.

This signal is then amplified, inverted (in 87'), and used to releasethe corresponding stop lever 4, thereby decoding the original butteredcode and registering it as a type face alignment ready to print. I i

In FIG. 1 it may be seen that the main or sustaining potential source 80is impressed between a common ground 96 and, through normally closedreset switch 79, the common interconnection of the six load resistors 78 which serve the common six wire signal bus 82.

Oneside of each glow tube 83 is connected to ground through lead 94 andcommon column loadresistor '93. The remaining side of each glow tube 83is connected to one of the six bus leads 82 corresponding ,to its orderof binary code representation. r r i All of the load resistors 93' andthe bus load resistors 78 ape made to be of suihciently low value withrespect to the total possible glow currents so that negligible voltagedrops occur across them due to glow currents alone.

The potential of battery 80 is chosento be less than the ignitionpotentials of tubes 83, but greater than their extinction potentials.Under these circuit circumstances, once any glow tube 83 is ignited, itwill remain so until switch 79 is opened at the end of the reset motionof mechanical connection 38, and after the printing action of hammers 40at which time all tubes 83 will be reset to extinction.

The distribution of the incoming signal information to the memory glowtubes 83, and to the hammer enabling memory coils 54, is accomplished bythe electrical switch commutators 89 and 88 respectively, both beingunder direct drive from shaft 66. Also mounted on the continuouslyrotating shaft 66 is the conventional analog to digital coding disk 69which signals via brushes or photocells 70 and leads 71 to the computer92 what the instantaneous position of the distributing switches 88-39may be, and at what point the engagement of the onerevolu-tion clutch 64may take place.

Since the computer 92 also has access, via the common stop coil bus 13,to phase switch 59, it knows the instant at which printing and resethave occurred, and can proceed to actuate switches 74 via printer inputbus 73 so as to emit the proper code signal group which it desires todistribute to the columnar position progressively signalled to it bycoding disk 69.

Switches 74 are shown in FIG. 1 as physical switches for simplicity. Inpractice, these switching -means 74 would comprise computer-controlledcurrent gates, preferably using solid state components. Diodes 76 areprovided to prevent sneak circuits.

When any watch 74 is closed by the computer, it raises the potentialofthe corresponding bus wire 82, relative to ground .by an amountdetermined by the current drop in l the corresponding load resistor 78due to current supplied printed corresponding to the given code. ofsuch' a signal is taken to mean the command for an by current source 77.This signal bus potential rise is designed to be less than thedifference between the potential of battery 80 and the firing potentialof any glow tube 83. Consequently, by itself, the closing of any switch74 cannot fire a glow tube 83.

Similarly, when the distributing switch :arm 89 arrives at the lead 94corresponding to a given column, current flows from current sourcethrough load resistor 93 in such a direction as to raise the potentialappearing across the glow tubes 63. Again, this potential rise isdesigned to be less than the difference between the potential of battery8i and the firing potential of any glow tube $53, so thatdistribution-enabling switch 89 by itself cannot fire a glow tube 83.

However, the actions of switches 89 and 7 4 are not only independent,but also additive, so that by choosing the correct design parameters itis possible by switch 89 to enable one column at a time, in sequence, toreceive glow tube ignition signals over common bus 82, since thecoincidence of the additive signals at the currently addressed columnwill then exceed the ignition voltage of tubes 83.

Once ignited, source Sit will sustain the discharge through the periodof optical comparison, and until the opening of reset switch '79extinguishes all tubes 83 for a new distribution cycle.

Switch 83 is-synchronized with switch 89, and serves to distribute theoutput of the diode or gate 75 tothe hammer enabling coil 54corresponding to a given column. In this Way, current from source 77will flow to a coil 54 during visitation by switch 88 only if a codesignal over bus 73 was received, implying that a character was to be Theabsence unprintedispace, and the corresponding hammer is prevented fro mimpactingthe paper by default of a release of its enabling lever 45.

'The returnlbus 13 from stop' coils 12, and the return bus 55 from thememory-enabling coils 54 are intended to extend to the correspondingcoils belonging to all the remaining columns. i r Similarly, theleads9i3 and 91 extend to the'corresponding tube group enabling circuitsand hammer enabling circuits, respectively, ofthe remaining columns;

As had been indicated, the leads of bus $2 also extend to all thememory-comparator tubegroups of the remaining columns. Evidently,although there is a separate load resistor 93 for each tube group, thereis only one common set of resistors 78, diodes 76, and gate diodes 75for the whole system. t

When the computer has completed its line signal distribution, assignalled to it by the positional code of disk 69, it may energize theone-revolution clutch coil 65, thereby initiating the mechanicalselection and reset cycle.

This selection cycle comprises a comparison operation in which theelectrically stored patterns of optical glow tube code information arerepeatedly compared by photoelectric means to the patterns of a decodingdisk 86 which moves synchronously with shaft 3 and its frictionallymounted type wheels 1.

The optical de-coding disks 86 shown in FIGS. 1, 2, and 3 are mountedeither integrally on shaft 3 by clamping spacers 97 as shown, or, if amore compact design is desired, on a separate countershaft which ismechanically coupled at unity ratio to shaft 3.

Also for the sake of compactness, a means has been devised to permit onede-coding disk 86 to serve the com parators of four columns. Thus, in atypical 100 column i photoelectric cell 85.

machine, there would be 25 such parallel disks. Each decoding disk is aphotographically prepared transparent substratefid on which the tenconcentric opaque coding track patterns M2. through ill have beendeposited.

The six glowtubes 33 associated with a one'coium'n butter memoryaremounted within an. opaque plastic moulding 93, which also forms thehousin for comparison photoelectric cell $5, and the support for theplastic moulded light pipe 34. The light guiding pipe 8 for eachmemory-comparison head 93 is made of a highly refractive plasticmaterial such as Lucite, and preferably is provided with an evaporatedmetal film coating except at the entrance and exit light ports, whichare given a ground translucent finish. The six entrance ports 99 on eachlight pipe are located opposite six corresponding holes in moulding 98leadingto: a glow tube housing about the parallel decoding disks 86.

Since the disk 36 is divided into 64 coding positions to accommodate the64 character (1 blank) type wheels, and

since there are four equally spaced comparison reading stations, itfollows that the tour lowest orders of coding (132, 1%, 19 i435) can beshared on the same physical coding tracks since the fourth binary orderfrom the lowest corresponds to l s of the circle, and to readingstations of a circle apart, the binary code patterns would lookidentically cyclic.

The fifth order tracks would look identical to heads 180 .apart', and soonlytwo varieties of the fifth order need be providedfldfi, lit?) so asto be 90 out of phase with one another. Track 1% serves heads 98 and93", while track M37 serves heads 98 and 98".

Finally, the sixth binary order tracks, subtending 180 as they do, lookdifferently in phase to each of the 4 heads, so that four phasewarietiesof siXth order tracks 1%, 109, 110, and 111 are provided to serve heads98,

7 9819 8 and 93" respectively.

By thus sharing the fourlowest orders of coding, and throw i e (Six flipflops) in Place/Of the Six singlg by partially sharing the. fifth order,the. comparatormernory assembly achieves a greatly improved compactness.i

' As shown in FIG. 2, the coding disk 86 is in the home position, andthe light pipe entrance ports 99 are all partially. uncovered by theopaque coding areas, so that theignition of any one glow tube memory inany headnis the only condi-tionnecessary to energize the corresponding'Ihe inverting amplifier 87, consisting of a singlestage of transistoramplification, is arranged to cut on its output'current to its stop coil12 I whenever i'tsphotocell 85 seeslighh'and to pass output current to.coil 12. when it sees darkness.

Consequently, if the computer had distributed the code commanding theprinting of the seventh character from home position into amemory-comparison head 93, it would have electrically ignited andoptically lit, the three lowest order glow tubes lying on code tracks102., 103 and 104, corresponding to the binary weights 1, 2, and 4respectively. I

For this reason, as the coding disk 86'stants to'rn'ove counterclockwisein response to the tripping of clutch 46 away'from the home positionillustrated, the light from the glow tube illuminating track 102 will becut off from access to photocell 85 after disk fid has moved of arevolution (orto the first character position).

However, the light from the glow tubes illuminating tracks 103 and 104at point are still unobscured, and. since photocell 85 is still seeinglight, coil 12 is unenergized, and lever 4 continues to be magneticallyrestrained. As disk 86 continues to the second character position,channel 193 will close, but channels 102 and 104 will still transmitlight to photocell 85, so the corresponding type Wheel 1 continues tofollow shaft 3 and decoding disks 36. At the third character position,track-s lit; and 103 will be blocked, but-track 1% will prevent releaseof the stop lever 4. g

In like manner, this interrogation willcontinue to find at least oneglow tube capable of blocking release of stop Evidently, the engineeringdesign of the systemmust take into account the speed of response of thephotocell and stop lever system, as well as the physical dimensions andtangential velocity of the teeth of type wheels 1, so that sate marginsfor reliable operation will result.

It is to be noted especially that the unambiguous operation of thissystem requires the choice of code sequence taught by my invention. Thissequence is one in which the order of initial binary coding channelobscuration progresses firom the lowest order toward the higher orders.This may be understood from the foregoing example'in which theelectroaoptical code for seven" was set up by lighting the three lowestorders of glow tubes 83. It, in this example, the decoding disk 86 hadbeen moved in a clockwise instead of counterclockwise direction, asignalof total darkness-causing release of lever 4 Would'have been receivedimmediately after A of a clockwise revolution even though thisdisplacement led to the wrong-character 64. This false signal isobviously due to'the fact that no means has been provided to distinguishbetween darkness due to an unlit tube behind an open code window anddarkness 'due to a littube behind a closed code window. V, p

In order to provide such distinction optically, using the samephotocell, a system of .12 code channels would have to beprovided-together with the equivalent of six double The' presentinvention avoids thiscornplexity, ands/till avoids aimbiguty, bychooseing the foregoing specification for the progression of initialobscuration in the several binary orders of coding. r

, The operation of my inventionis as follows: .When 7 the signals 71 and13 infonrn the computer 92. that the printer is free to receive a newline of printing, the cornputer may distribute parallel (or fast serial)groups of six binary code signals over bus 73 to switch-means 7 4at'the,

moments "signalled to it by disk 69 (through bus 71) at which switches87 and 89 are enabling the printing column in which the coded characteris to be printed.

The switching means 74in response to these signals produces pulses onthe common bus 82, which in turn,

ignite the code pat-tern of glow tubes 85 in the memory head 98corresponding to the column which distributing switch 89 is momentarilyenabling.

Coinciden-tally with the distribution of any character code to a memoryhead 98, gate 75- release the correspond;

ing hammer enabler 45 viaswitch 88, bus 55, and coil 54.

This distribution process continues until the memory heads 93 are filledwith luminous discharge patterns reprotation of shaft 32 and crank pin28. This causes shaft 3 together with decoding disks 86 and frictionfingers '14 to move first counterclockwise, carrying with them the typewheels 1.

As decoding disks 86 interrogate the luminous memory code patterns foreach column, character by character, there will come an instant for eachcolumn in which agreement will be signalled in the correspondingcomparator photocell 85 by the occurrence of darkness. This successfulcomparison signal for each column, in turn, will release thecorresponding stop lever 4, and so align the commanded line of typeWheels 1.

At the end of the counterclockwise selection phase of the reciprocationof shaft '3, cam lobe30 efiects the impacting on paper 18 of thosehammers 40 which have been selected, thereby printing the selected'line;

The continuing action of lobe 30 then resets the hammer-enabling levers45 and the stopping levers 4, and extinguishes the entire bank of memoryglow tubes 83 by the momentary opening of switch 72.

Continued rotation of crank pin 28 then returns type wheels 1 to theirhome position, while disabling the stop coils 12 by means of camoperated switch 59.

At the end of the revolution of shaft 32, the ratchet mechanism 20advances the paper 18 by one line, in preparation for the next printingcycle.

During the return reciprocation of shaft 3, the com puter 92 is free torefill the buffer memory heads 98 with the coded signal informationrepresenting a new printing line.

To those skilled in the art, many modifications and substitutions willbe obvious within the broad scope of my invention, and it is notintended that the specific disclosure here detailed shall limit thescope of the claims.

What I claim is: V

1. In a line printer, the combination comprising: a plurality ofparallel coaxial rotors bearing type faces on their peripheries; torquemeans'to urge said rotors onto angular rotation about'said axis in acharacter selective direction; a character scanning rotor; means toreturn said rotors to a home position; at least one decoding disk; meansto rotate each said decoding disk in synchronization with said characterscanning rotor during its selective direction of rotation; atleast onearcuate binary decod ing channel on each said decoding disk, each saidchannel having alternate window sectors and opaque sectors; a group ofgas discharge tubes corresponding to each of said type face rotors, eachtube being located adjacent to a code channel in said decoding disk;means to electrically ignite selected ones of said gas discharge tubegroups in accordance with a coded line of character information to beprinted; means to sustain the discharge of said tubes after said codedignition whereby to maintain a corresponding pattern of light signalsfrom each of said groups of tubes during selective rotation of saidcharacter scanning rotor; a photoelectric cell corresponding to eachsaid group of gas discharge tubes; optical means to convey the lightpassing from any discharge tube within a group through a window in saiddecoding disk channel to the photocell corresponding to the said group;a separate electromechanical means to stop the selective rotationaladvance of each rotor in response to an electric stop signal; and meanscorresponding to each saidphoto cell responsive to the intervention ofan opaque sector of said decoding channel between each energized tubewithin the corresponding group and said corresponding photocell forgenerating an electric stop signal whereby to actuate saidelectromechanical stop means.

2. In a line printer in accordance with claim 1: a ham mer correspondingto each said rotor; a normally disabled means associated with each saidhammer for impelling it towards the corresponding said type rotor; abinary memory device for each said hammer; means responsive to theobverse condition of said memory device to enable said impelling means;means to reset said .to disable said electromechanical stop means duringthe action of said rotor return means.

5. In a line printer in accordance with claim 1: a common inputsignalbus havingas many conductors as there are tube members in each saidgroup; and means for distributing ignition signals from said bus toignite the tubes in said groups serially in accordance with the signalsappearing on said bus.

6. In a line printer in accordance with claim 1: a drive shaft; meanscontinuously to rotate saiddrive shaft; a first driven shaft;incremental trip clutch means for coupling said driven shaft to saiddrive shaft for a fixed predetermined angular displacement; means fortripping said clutch; a second driven shaft; means to couple saidscanning rotor to said second driven shaft during the said selectivedirection of said scanning rotor; means to couple said rotor returnmeans to said second driven shaft during the return of said rotors tosaid home position; and

means to reciprocate said second driven shaft through a fixed angulardisplacement in response to the said incremental advance of said firstdriven shaft.

7. In a line printer, the combination comprising: a plurality ofparallel coaxial rotors; a plurality of character type faces located onthe periphery of said rotors; means to urge said rotors into angularrotation about said axis in a character selection direction; a characterscanning rotor; means to return said rotors to a home position; aplurality of decoding disks; means to rotate said decoding disks insynchronization with said scanning rotor during its selective directionof rotation; a plurality of concentric decoding channels on each of saiddecoding disks, each of said decoding channels representing a binaryorder of coding, and each channel having alternate window sectors andopaque sectors; a group of gaseous discharge tubes corresponding to eachof said type rotors, each tube within a group being located adjacent toa different decoding channel in said decoding disk; means electricallyto ignite selected ones of said gaseous discharge tube groups inaccordance with. a coded line of character information to be printed;means to maintain the discharge of said tubes after said coded'ignitionwhereby to maintain a corresponding pattern of light signals from eachof said groups of tubes. during selective rotation of said scanningrotor; a photoelectric cell corresponding to each said group-v ofdischarge tubes; optical means to convey the light passing from anydischarge tube within a group through a window in said decoding disk tothe photocell corresponding to said group; a separate electromechanicalmeans to stop the selective rotational advance of each said type rotorin response to an electric stop signal; and means corresponding to eachsaid photoelectric cell, responsive to the intervention of an opaquesector of said deco-ding channels between each energized tube within thecorresponding group and the said corresponding photoelectric cell, forgenerating an electric stop signal whereby to actuate saidelectromechanical stop means.

8. In a line printer in accordance with claim 7: said tube groups beingarrayed substantially radially relative to said concentric channels;said window channel sectors subtending angles equal to the anglessubtended by said opaque channel sectors; a plurality of said tubegroups being associated with each decoding disk and equally spacedthereabout by an even number of the lowest order 11 sector widths; thecodes of each of the said channels associated with a given group being adifferent binary order; and each of the said tube groups associated witha given disk sharing a number of channels equal to the number of suchgroups associated with each disk.

9. A printer comprising: a moveable type member hearing spaced typefaces representing a plurality of characters and constrained to move ina path which causes said typefaces to ,moveserially into registrationwith a printing station; a hammer; a web; means to. impress said Webbetween said hammer and one of said typefaces at said printing station;means to restore said type member to a home position; scanning means tourge said type member tg' move in ajcharacter selecting direction awayfrom said home position; stop means to arrest the motion of said typemember; a spaced array of gaseous discharge tubes; a moveable codingmask having a pluralityof" parallel coding channels corresponding toeach said tube and each said channel comprising an alternating sequenceof opaque areas and of window areas; said coding mask being constrainedto move so that each channel uniquely masks and unmasks each said tube;means to move said mask in synchronism with said scanning rotor;electrical means to ignite a selected pattern of said discharge tubes; aphotoelectric cell; optical means to convey the light from those ignitedsaid tubes which are adjacent to a window area of said mask to saidphotoelectric cell; and means responsive to the occurrence of darknessat said photoelectric cell to actuate said stop means.

10. A printer comprising: a moveabie type member bearing spaced typefaces representing a plurality of characters" and constrained to move ina path which causes said type faces to move serially into registrationwith a printing station; hammer means to effect the printing of the oneof said type faces which is in registration with said printing station;means to restore said type member to a home position; scanning means tourge said type member to move in a-character selecting direction awayfrom said homeposition; stop means to arrest the motion'of said typemember; a spaced array of light sources; a moveable coding mask having aplurality of parallel coding channels corresponding to each said lightsource and each said channel comprising an alternating sequence oropaqueareas and of window areas;'said coding mask being constrained tomove so that each said channel uniquely masks and unmasks each saidsource; means to move said mask in synchronism with said scanning rotor;electrical means to energize a selected pattern .ofsaidlight sources; aphotoelectric cell; optical means to convey 'the light from thoseenergized sources which are adjacent to a window area of said mask tosaid photoelectric cell; and means responsive to the occurrence ofrelative darkness at said photoelectric cell to actuat said stop means.1

References Cited in the file or this patent UNITED STATES PATENTS JonesFeb. 27,

1. IN A LINE PRINTER, THE COMBINATION COMPRISING: A PLURALITY OFPARALLEL COAXIAL ROTORS BEARING TYPE FACES ON THEIR PERIPHERIES; TORQUEMEANS TO URGE SAID ROTORS ONTO ANGULAR ROTATION ABOUT SAID AXIS IN ACHARACTER SELECTIVE DIRECTION; A CHARACTER SCANNING ROTOR; MEANS TORETURN SAID ROTORS TO A HOME POSITION; AT LEAST ONE DECODING DISK; MEANSTO ROTATE EACH SAID DECODING DISK IN SYNCHRONIZATION WITH SAID CHARACTERSCANNING ROTOR DURING ITS SELECTIVE DIRECTION OF ROTATION; AT LEAST ONEARCUATE BINARY DECODING CHANNEL ON EACH SAID DECODING DISK, EACH SAIDCHANNEL HAVING ALTERNATE WINDOW SECTORS AND OPAQUE SECTORS; A GROUP OFGAS DISCHARGE TUBES CORRESPONDING TO EACH OF SAID TYPE FACE ROTORS, EACHTUBE BEING LOCATED ADJACENT TO A CODE CHANNEL IN SAID DECODING DISK;MEANS TO ELECTRICALLY IGNITE SELECTED ONES OF SAID GAS DISCHARGE TUBEGROUPS IN ACCORDANCE WITH A CODED LINE OF CHARACTER INFORMATION TO BEPRINTED; MEANS TO SUSTAIN THE DISCHARGE OF SAID TUBES AFTER SAID CODEDIGNITION WHEREBY TO MAINTAIN A CORRESPONDING PATTERN OF LIGHT SIGNALSFROM EACH OF SAID GROUPS OF TUBES DURING SELECTIVE ROTATION OF SAIDCHARACTER SCANNING ROTOR; A PHOTOELECTRIC CELL CORRESPONDING TO EACHSAID GROUP OF GAS DISCHARGE TUBES; OPTICAL MEANS TO CONVEY THE LIGHTPASSING FROM ANY DISCHARGE TUBE WITHIN A GROUP THROUGH A WINDOW IN SAIDDECODING DISK CHANNEL TO THE PHOTOCELL CORRESPONDING TO THE SAID GROUP;A SEPARATE ELECTROMECHANICAL MEANS TO STOP THE SELECTIVE ROTATIONALADVANCE OF EACH ROTOR IN RESPONSE TO AN ELECTRIC STOP SIGNAL; AND MEANSCORRESPONDING TO EACH SAID PHOTOCELL RESPONSIVE TO THE INTERVENTION OFAN OPAQUE SECTOR OF SAID DECODING CHANNEL BETWEEN EACH ENERGIZED TUBEWITHIN THE CORRESPONDING GROUP AND SAID CORRESPONDING PHOTOCELL FORGENERATING AN ELECTRIC STOP SIGNAL WHEREBY TO ACTUATE SAIDELECTROMECHANICAL STOP MEANS.